Tuberculosis vaccine strain _Mycobacterium bovis_ BCG Russia is a natural _recA_ mutant

The current tuberculosis vaccine is a live vaccine derived from _Mycobacterium bovis_ and attenuated by serial _in vitro_ passaging. All vaccine substrains in use stem from one source, strain Bacille Calmette-Guérin. However, they differ in regions of genomic deletions, antigen expression levels, immunogenicity, and protective efficacy. As a RecA phenotype increases genetic stability and may contribute restricting the ongoing evolution of the various BCG substrains, we aimed to inactivate _recA_ by allelic replacement in BCG vaccine strains representing different phylogenetic lineages (Pasteur, Frappier, Denmark, Russia). Homologous gene replacement was successful in three out of four strains. However, only illegitimate recombination was observed in BCG substrain Russia. Sequence analyses of _recA_ revealed that a single nucleotide insertion in the 5' part of _recA_ led to a translational frameshift with an early stop codon making BCG Russia a natural _recA_ mutant. At the protein level BCG Russia failed to express RecA. According to phylogenetic analyses BCG Russia is an ancient vaccine strain most closely related to the parental _M. bovis_. Our data suggest that _recA_ inactivation in BCG Russia occurred early and is in part responsible for its high degree of genomic stability, resulting in a substrain that has less genetic alterations than other vaccine substrains with respect to _M. bovis_ AF2122/97 wild type

High-pressure Debye-Waller and Grueneisen parameters of Au and Cu

The lattice vibrations are determined in the quasi-harmonic approximation for elemental Au and Cu to twice their normal density by first-principles electronic band-structure calculations. It is found for these materials that the important moments of the phonon density of states can be obtained to high accuracy from short-ranged force constant models. We discuss the implications for the Grueneisen parameters on the basis of calculated phonon moments and their approximations by using bulk moduli and Debye-Waller factors.Comment: 4 pages, 2 figures to appear in the proceedings of the 13th APS Topical Conference on Shock Compression of Condensed Matter (scheduled for April 2004

Automated mass spectrometer/analysis system: A concept

System performs rapid multiple analyses of entire compound classes or individual compounds on small amounts of sample and reagent. Method will allow screening of large populations for metabolic disorders and establishment of effective-but-safe levels of therapeutic drugs in body fluids and tissues

Slabs of stabilized jellium: Quantum-size and self-compression effects

We examine thin films of two simple metals (aluminum and lithium) in the stabilized jellium model, a modification of the regular jellium model in which a constant potential is added inside the metal to stabilize the system for a given background density. We investigate quantum-size effects on the surface energy and the work function. For a given film thickness we also evaluate the density yielding energy stability, which is found to be slightly higher than the equilibrium density of the bulk system and to approach this value in the limit of thick slabs. A comparison of our self-consistent calculations with the predictions of the liquid-drop model shows the validity of this model.Comment: 7 pages, 6 figures, to appear in Phys. Rev.